Does this show overfitting?

[Billy-ZTB]

I used a VGG16 based UNet to learn to segment buildings from an image. During training, I found that the encoder's activation starts to shrink to small area of the buildings, and also show up on some background area, does this show that my model is overfitting?

Examples from epoch 5 and epoch 24:

Epoch5:

Epoch 24:

Epoch5:

Epoch24:

Epoch5:

Epoch24: